The invention relates to a hole-shaping and thread-forming screw with a non-cutting hole-shaping end section that ends in a point or a point-like shape, a shaft section provided with a thread, and an engagement section for attaching or inserting a tool, as well as a method for driving in a hole-shaping and thread-forming screw.
In the case of thread-shaping screws, which drill their own hole or shape it without cutting, it was standard procedure until now to manufacture the hole-shaping end section of a material that could be hardened, in other words carbon steel. In most instances, expensive solutions were provided, if the head and partial sections of the shaft had to be manufactured from a stainless material. In addition, welding solutions were used, where a drill tip of material that could be hardened, in other words carbon steel, was welded to the other region of the screw.
This not only requires several work steps, it also results in particularly high manufacturing costs.
The present invention has therefore set itself the task of creating a possibility, for a screw made of stainless steel, of shaping a hole with this screw, without having to use welding solutions with different materials.
According to the invention, it is proposed that the non-cutting hole-shaping end section, which narrows at an acute angle towards the end, relative to the screw axis, is formed of a stainless material.
Screws with the embodiment explained initially have become known in various embodiment variants. For example, in U.S. Pat. No. 2,015,159, a fastener is shown and described, which has a nail tip and a corresponding thread on the shaft. By hitting the screw with a hammer, the tip is forced through a thin metal sheet, and subsequently it is driven in by means of a corresponding rotational movement of the threaded section. This combination of a nail and a screw was surely manufactured of a carbon steel at the time of the application, since there was probably no idea of stainless attachment elements at that time. From EP-B1 0 464 071, a hole-shaping and thread-forming screw is known, which has a hole-shaping part that narrows, where the screw is made in one piece of annealed steel. By means of rotation of the screw, friction surfaces are formed between the screw and the sheet metal to be passed through, so that the metal sheet is heated in such a way that the material is brought into its plastic range, in that it becomes so resilient in the radial direction that the desired hole expansion with material displacement to form a nozzle occurs. In this embodiment, also, an attempt was made to reach a solution with a carbon steel.
With the present invention, the possibility is created, for the first time, of shaping the hole for the thread-cutting screw with a corresponding end section made of a stainless material. Until now, it was considered impossible, by persons skilled in the art, to shape a hole with a screw made of a stainless material. Rather, it was always assumed that a drilling process or a corresponding high level of heating, up to the plastic range, was required, in order to be able to drill or simply shape a hole. A person skilled in the art had to assume, until now, that a drilling process with corresponding xe2x80x9ccutting edgesxe2x80x9d made of stainless steel is completely impossible, and that the use of carbon steel, in other words annealed steel, is required for shaping a hole without using drill blades.
The present invention has therefore overcome a prejudice of persons skilled in the art, because it was made possible to shape the hole with a screw made of stainless material, and furthermore also a stainless end section, to form the thread, and therefore to be able to use a fastener which is entirely formed of stainless material.
Therefore it is also a particular characteristic, according to the present invention, that all the sections of the screw are entirely made of a stainless material.
It is possible that a stainless steel is used as the stainless material, or that light metals or alloys of light metals, i.e. alloys with a major proportion of light metals, e.g. brass, copper, aluminum, or similar metals, are used as the stainless material. Depending on the specific purpose of use, the structure according to the invention results in very specific possibilities of use of a screw made of a special material. For example, it has now become possible to make the material selection with mutual adaptation of the work piece and the screw, without any special welding solutions or the attachment of drill plates of different materials being required.
For the hole-shaping end section, various embodiment variants are possible, with different design variants resulting as a function of the material of the work piece and, of course, as a function of the material of the screw. For example, it is possible that the non-cutting hole-shaping end section is formed from two or more partial sections with different angles relative to the screw axis. In this connection, it is also possible that the non-cutting hole-shaping end section is made to be triangular or polyangular, circular, ellipsoid, of a constant diameter, or similar in cross-section.
It is particularly advantageous if a special method is used to drive the screw in. According to the invention, it is proposed in this regard that when the screw is driven in to shape the hole in non-cutting manner, an axial impact effect is exerted on the screw in addition to the rotational drive. It has been shown that the additional impact effect is particularly advantageous, specifically when using screws made of stainless material, and that it results in rapid penetration of the work piece without significant heat development.
Furthermore, the additional process step that the impact effect on the screw acts only during the hole-shaping process and is eliminated during the thread-cutting process and while the screw is driven into the thread, is advantageous. In other words, once the hole has been shaped, the impact effect is removed, so that the thread can be formed in optimum manner. This results in an optimum fit, particularly during thread forming, and the fact that the hole wall has been partially elastically deformed during the preceding hole-shaping process also contributes to this fit, so that now this hole wall is more or less resiliently pressed against the thread.